1. Field of the Invention
The present invention relates to a technology for dividing an original picture inputted for each frame into motion compensation blocks and encoding each motion compensation block using motion compensation inter-frame prediction.
2. Description of the Related Art
Currently, a variety of methods are developed for the encoding of a moving picture. Such an encoding method includes one method for dividing an original picture to be encoded into motion compensation blocks and encoding each of the motion compensation blocks using motion compensation inter-frame prediction. The motion compensation inter-frame prediction is conducted by detecting the motion vector of a motion compensation block between consecutive frames.
In a moving picture (video), a variety of special-effect scenes are used as requested. In that case, fade scenes, such as fade-in or fade-out, are sometimes inserted as such an effect scene. In the encoding method using the motion compensation inter-frame prediction, it is known that a prediction error between frame increases in such a fade scene. In the assumption to maintain the same picture quality, the amount of data (information) of encoded data (amount of codes) obtained by encoding an original picture increases as a prediction error increases. Therefore, the conventional moving picture encoding device includes one which suppresses the degradation of picture quality by detecting a fade scene and adjusting the amount of data assigned to data to be encoded (Japanese Patent Application Publication No. 2000-59775).
In the fade scene, the entire brightness of an original picture sequentially changes. In the conventional moving picture encoding device set forth in Japanese Patent Application Publication No. 2000-59775, such a characteristic is focused and a fade scene is detected. The conventional moving picture encoding device set forth in Japanese Patent Application Publication No. 2002-51341, furthermore a motion vector is focused and a fade scene is detected. When a fade scene is detected, a motion vector is avoided from being encoded by compulsorily setting it to a zero level (corresponding to assigning a 0 point being the original position) and the amount of data to be encoded (amount of codes) is suppressed.
The conventional moving picture encoding device set forth in Japanese Patent Application Publication No. 2002-51341 can detect a fade scene with higher accuracy than the conventional moving picture encoding device set forth in Japanese Patent Application Publication No. 2000-59775, furthermore by focusing on a motion vector. However, actually sufficient accuracy cannot be obtained yet. Therefore, it is desired to a fade scene with higher accuracy.
In the encoding method using motion compensation inter-frame prediction, a difference (error) between an original picture and a predicted picture is encoded. In Japanese Patent Application Publication No. 2002-51341, in order to avoid the selection of an unnecessary motion vector, the motion vector is compulsorily made a zero vector. However, when the motion vector is made a zero vector, there is a possibility that the error increases. When the error increases, the amount of data (information) which is assigned to the amount of codes in order to suppress the degradation of picture quality increases. Thus, in order to more appropriately encode data when detecting a fade scene, the selection of an unnecessary motion vector must be avoided and also the degradation of image quality must be more avoided.